Process for treating iron



"Patented Feb. 2 3, 1926.

"UNITED" STKTES.

PATENT OFFICE.

' WILLIAM-J. DIEDERICHS ANSON HAYES, OF AMES, IOWA.

, :enoenss non '1REATING men.

No Drawing. Original application filed August 21, 1922, Serial No. 583,370. Divided and this applicationfiled August 6,' 1925. Serial No. 48,624. I

To all whom it may concern." a Be i known that we, WILLIAM J. Dinon moHs .and ANSON HAYES, citizens of the United States of America, and residents of Ames, Story County, I owa, have invented a new and useful Process'for Treating Iron, of which the following is a specification.

The subject matter of this application was originally included in but has been divided from our application filed August 2l, 1922, Serial Number 583,370;

' in our parent application above referred to.

However this may bedone at times if desired, but by omitting it considerable time may be saved. When the packing is omitted the-white iron castings may be supportedin.

any Suitable manner in the furnace to prevent sagging and warping iunder'the intense heat. a

The process consists in heating for any length of time, raising the temperature of the white iron castings with convenient,

The object of this invention is to provide rapidity, either rapidly or slowly; to any breaking. I"

This and other objects of the inve ntion will be more clearly described in the speci-' fication and pointed out in the appended claims. I

Any suitable type or'form of furnace or so-called annealing oven may be employed in carrying out our improvedprocess, and

may be'heated by any of the well known fuels such as gas, oil, or powdered coalburned in connection with air; or the heat may be secured electrically or by a combination of combustion and electricity, orin any other manner that may be desired 'so long as the desired temperatures and atmospheres are secured. v A,

The iron used in this processflis known as white cast iron, differing principally from ordinary gray iron in that while bothcontain carbon, the white. cast iron contains the carbon wholly or principally in the form of earbid of iron represented'by the formula Fe C, while gray cast iron containsthe carbon to a greater degree in the form of graphite or, graphitic carbon.

Through the nse of this process we obtain' a product having a higher tensile strength than white cast iron and under ,certain conditions of procedure also having considerable ductility or ability tofb end. and

castings in boxes or .pots containing, the.

packing material, as is done on the ordinary malleabilizing process as referred to point between the critical temperature ofthe material (about 740 degrees centigrade) and the point of incipient fusion, and holding at the chosen higher temperature for a period of fifteen minutes to five hours, or more. The actual time required will de pend. upon the temperature chosen, lower temperatures requiring longer times, and upon the chemical composition of the white iron being treated. In any case it is only desired to maintain the higher temperature until themassive cementite is practically all absorbed in the solid solution. We are satisfied that in most instances it would avail little to hold at the higher temperature for a longer period than about five hours, since ractically all of the desirable change would have occurred in that 'vtime, especially if the high temperature employed is above 900 de-' grees Centigrade; and that holding for longer periods would result only in a wastemassive cementite into the solid solution will p be very materially increased. y

The material is thencooled either rapidly 0r-slowly to a temperature in the neighborhood of the critical temperature, either within or outside of the heating furnace.

This cooling inay be accomplished, ifdesired, in successive steps and holding for an appreciable time at each successive step, until a temperature in the neighborhood of the critical has been reached. This may be:

carried out in practice byholding three. or

four furnaces at the various temperaturese desired and. transferring the material successively fromon'eto the next, which would.

usually be .done'without lowering'-the--tem---.

perature of the castings below that of the next furnace during such'transfer. We do not wish, however, to be limited to this method of cooling to the nei hborhood .of the critical temperature. T may be cooled in the furnace," or they may 7 be removed and cooled to a temperature below that of the next gemperature to which the material is to be reated, by quenching in any suitable material such as sand, cement, powdered mica or the like. The operations of heating and cooling may be repeated for any desired number of .repeti-' tions, that is to say the material may be alternately heated to a point above thecritical temperature'and cooled to a temperature in the neighborhood of the critical. It has .been demonstrated by experiment that the resultant product is an iron ossessing con-- siderably greater strength t an the white iron castmgs and also having a consider-- able degree of ductility. The number of repetitions or alternate heati s and coolings, as well as the rates of eating'and cooling, may be varied in accordance with the properties desired in the product. Our ex riments show that the variations above re erred to in the treatment of the iron result in castings possessing (1') a high tensile to eight percent elon ationor I coolin with a heating as that obtained by either one oithe methods strength, of 85,000 to 90,000 pounds per square inch, with no ductility; to (2) those ha a strength of about 60,000 to 85,000 poun s per square inch or more, withtwo more. We have also foun that b a combination of the high temperature ollowed by a repetition of alternate heating and cooling; or vice versa, that is alternate heating and to, higher tempera; osed, we obtain a ture ollowing 'or inte f t e same properties resulting material 0 individually.

In-speakmg of the critical temperature of the material it should be borne 1n mind,

a as is well known in metallur that the critical temperature can -be, an is undercooled by a re id cooling, and therefore willbe reduced y heating to .a temperature .above the critical and cooling fairl rapidly;

so that in thereafter'heating to t e cr tical temperature, it is obvious that a lower actual temperature will be involved than the orig inal critical temperature. The lan ua eof this ecification' and the appende c aims is 11525 with this fact in mind and should beso construed.

As a concrete example of what we have obtained in. our ex eriments, we give. the following by way 9 illustration only. Bars of white cast iron were heated at 10001 degrees centigradefor one hburfiwere cooledto 850 degrees centigrade with the and held at such tem fqrnac'e erature. for sixours, and then were coole inthe furnace to below the critical temperature. 'The materialhe castings inches.

tion d'fproperties produced as the final rate 600 pounds per square inch and an elongation of five percent in two inches.

Likewise by way. of illustration, bars were alternately heated in the furnace to 850 degrees centigrade and cooled in the furnace to-about 650 degrees centigrade, for a number. of repetitions. After thirteen such heatings and coolings the bars showed .a tensile strength of 70,500 pounds per square inch ;with five percent elongation in two inches; and after seventeen repetitions the showed 71,500 pounds per square inch wit five and one-half percent elongation A series of exper ments were conducted with white cast iron bars at various temperatures and with different rates of cooling. First they were heated three hours at 927 degrees centigrade, cooled to 849 degrees in forty-five minutes and left at that temperature for three hours and then" ooled to 649 degrees at the rate of 3.6 degrees per minute. The overall time required, was I eight hours, and the bars showed 'a tensile stren h of 74,400 pounds per .1 square inch and our percent elongation in two inches.

Next, bars were heated three hours at 982 degrees centigrade, cooled to 899-degrees in forty-five minutes and left'at that temperature for three hours and then cooled to 649 dqlgrees at the rate of 2.8 degrees per minute. T e overall time required was nine hours and the bars showe a'tensile strength oi 69,000 pounds per square inch aiid four and one-half percent elongation. Then bars were heated three hours at 982 degrees centigrade, cooled to 849 degrees in elghtz minutes and left at that temperature 0 and one-halt hours, then cooled to 649 degrees at the rate of 2.2 degrees per minute. he overall time required wasthirteen hours and the bars showed a tensile strength oi 60,380 pounds per square inch and an elon- Eation of six per cent. Finally, bars were eated three hours at 982'deg'rees centigrade cooled to 899 degrees in sixty minutes an left at that temperature for three hours, then cooled to 649 degrees at the rate of 1.7 de ees per minute. The overall time requ red was ten and one-half hours, and the bars showed a tensile strength of 56,600 pounds per square of eight and one-half per cent in two Attention is called to the gradaof cooling was made slower.

We claim as our invention p c -1. The process for the heat treatment of castings from white cast iron which consists in (1) subjectingfthe casting to a'temperathe tur'e above the critical temperature 0 material vfor a period of from fifteen minutes to five hours or more but r six.

inch and an elongation only until the iron carbid present is. practically all. absorbed in the solid solution, which means 'perature above the critical temperature of the material for a period of from fifteen minutes to five hours or more but only until the iron carbid-present is practically all absorbed in the solid solution, which means that in irons of commercial composition the combined carbon is reduced to approximately nine-tenths of one percent; (2) the cooling of the casting to a lower temperature in the neighborhood of the critical temperature; and (3) the cooling of the casting through a range from about 770 degrees to about 650 degrees Centigrade at a rate not less than about seven degrees centigrade per hour.

3. The process for the heat treatment of castings from white cast iron which. consists in (1) subjecting of the casting to a temperature above the critical temperature of the material; (2) cooling of the casting to a temperature in the neighborhood of the critical temperature by successive steps and holding for an appreciable time at each successive step, until a temperature in the neighf borhood of the critical hasbeen reached; and (3) cooling the casting to a lower temperature at a rate not less than about seven degrees centigrade per hour.

4. The process for the heat treatment of castings from white cast iron which consistsin (1) subjecting of thecasting to a temperature above the critical temperature of the material for a period of. from fifteen minutes to five hours or more, but only until the iron carbid present is practically all absorbed in the solid solution; (2) cooling of the casting by successive steps and holding at each successivestep for an appreciable time, until a temperature inthe neighborhood of' the critical temperature has been reached; and (3) the cooling of the casting to a lower temperature, at a rate not less than about seven degrees centigrade per I hour. 5. The process for the heat treatment of castings from white cast iron which consists in 1) the subjecting of the casting to a tem perature above the critical temper ture of the material; (2) the cooling of th casting to atemperature in the neighborhood of the critical temperature; (3) a repetition of the above named steps, alternately; cooling of the casting at a rate not less than about sevendegrees centigrade per hour.

Signed at Des Moines, in thecounty of Polk and State of Iowa, this 18th day of June, 1925.

ANSON HAYES.

and (4) the WILLIAM J. DIEDERICHS. 

